1. Technical Field
The field of the present invention relates generally to an apparatus for and a method of moving a slider for operating mating zipper elements along the mating zipper elements during the manufacture of a product that includes mating zipper elements operated by a slider.
2. Background Art
The manufacture of thermoplastic bags and other products containing mating zipper elements (i.e., a thermoplastic zipper typically having a rib and groove construction) is known in the art. Often, such mating zipper elements are operated by a slider. There are a wide variety of designs for such slider-zipper combinations. For example, U.S. Pat. Nos. 5,067,208; 4,262,395 and 5,283,932 show different types of sliders and mating zipper elements used in the construction of re-sealable thermoplastic bags. In these and other known arrangements, the sliders operate to connect and disconnect (depending on the direction of movement) opposing mating zipper elements as the slider is moved along the length of the zipper by a user. Thus, by moving the slider, the user can open or close the re-sealable thermoplastic bag or other such product.
In the manufacture of such thermoplastic bags, for example, a web of folded thermoplastic film is used to form a series of bags. Formed on ends of the folded thermoplastic film opposite the fold are corresponding mating zipper elements. As the film is fed through different stages in the manufacturing process in the direction of the fold, various assemblies perform tasks such as mounting the sliders on the zippers corresponding to separate bags, severing and sealing the film to form the lateral edges of the separate bags, and fusing specified lengths of the mating zipper elements to form the ends thereof. In a typical manufacturing process, the thermoplastic film is indexed to different stages in which individual components perform the different manufacturing processes described above.
Typically, the manufacturing system is set up such that the slider is properly positioned on the mating zipper elements as the film is fed through the system and processed in the different stages. However, it is possible that the slider may be mechanically forced out of position along the mating zipper elements during the manufacturing process.
Also, the slider could become out of position with respect to the manufacturing line. For instance, the film may be mis-fed or stretched due to a build up of tension in the film. Thus, while the slider may not move out of position along the mating zipper elements, the slider may be out of position with respect to the components or stages of the manufacturing line.
When mis-positioned, the slider has the potential of interfering with components of the manufacturing system. The interference can lead to damage to the slider, which would make the final product defective. However, when the slider is mis-positioned due to tension that stretches the film, the final product may be defective anyway because the film itself may not be properly processed.
Nevertheless, it is still important that the slider not be mis-positioned even when the end product will be defective. The reason being that the slider is typically made of a rigid plastic material that can damage or jam components of the manufacturing line if it interferes with the operation of those components.
For example, in one stage of manufacturing re-sealable thermoplastic bags including a slider-zipper combination, a folded web of thermoplastic film is laterally severed and sealed into segments which define the separate bags. As shown in FIG. 3, the typical mechanism for performing this process is a clamping device 200, which includes a pair of seal bars 30 separated by a gap, an electrically-heated hot wire 40, and a seal drum 20. The seal bars 30 intermittently contact the film and clamp it against the seal drum 20. Once clamped, the hot wire 40 advances through an opening in the surface of the seal drum 20, burns its way through the film, and moves into the gap between the seal bars 30. In this way, the film is severed into segments and the resulting severed edges are simultaneously sealed.
It is possible that the slider 50 may be mis-positioned with respect to the components for severing and sealing the film because the slider 50 is moved out of position along the mating zipper elements or because tension in the film causes stretching that mis-positions the entire film. In such an instance, the slider 50 may interfere with the operation of the components for severing and sealing the film, as shown in FIG. 3. In particular, the slider 50 may be clamped and crushed between a seal bar 30 and the seal drum 20, which can damage the hot wire 40, in addition to the slider 50 itself. Also, if the slider 50 is in the path of the hot wire 40, the hot wire 40 can be bent or snapped as it moves through the gap.
Accordingly, not only is it important to position the slider so it is not damaged by the machinery on the assembly line, but it is even more important to ensure that the slider is not in a position at which it can damage the machinery.
If the slider is accurately positioned with respect to the machinery and components of the manufacturing system, valuable time is saved by not having to shut down the system to repair damage that may be caused by the sliders. In addition, costs are reduced by increasing the life of the components that otherwise would need to be replaced because of slider damage.
Accordingly, there is a need in the art for a system for positioning the sliders along the mating zipper elements during the manufacture of products that include mating zipper elements operated by a slider, so as to not interfere with machinery used in the manufacturing process.